The invention includes embodiments that relate to an etchant, and to a method of etching. The invention includes embodiments that relate to a laminate formed by etching, and to a device incorporating the laminate.
Semiconductor crystals, and the like, may be grown on foreign substrates or support layers to form a laminate. A support layer may include, for example, sapphire (aluminum oxide), which may be used because of inherent physical and chemical properties of the aluminum oxide. Some end-use applications may require the removal of part, or all, of the support layer after the semiconductor layer is formed. The removal of the support layer from the laminate may be advantageous to the formation of microelectromechanical (MEMS) devices, semiconductor devices such as integrated circuits, and the like. However, the removal process may be problematic in that the semiconductor layer may be damaged, or the removal process itself may be undesirable.
Support layers may be removed by, for example, etching, laser ablation, or by mechanical means. Some materials may etch differently than others based on material type, type of etchant, process parameters, and the like. For example, polycrystalline aluminum oxide or amorphous aluminum oxide may have an increased surface area and decreased chemical bonding strengths relative to single crystal or quasi-single crystal aluminum oxide (sapphire).
Etchants and their methods of use may produce differences in the resulting freestanding or etched laminates. These structural, chemical and/or physical differences may affect one or more of electrical properties, optical properties, physical properties, and the like, and further may affect the response of the etched laminate in subsequent processing steps. Dry Etch is a process that may result in a selective removal of material from a substrate by using a gas or plasma. There are at least three commercially viable dry etching processes, each of which may be less economically advantageous relative to wet etching. Hydrogen fluoride (HF) may be used in chemical vapor phase etching, and xenon fluoride (XeF2) may be used to create isotropic etches. Sputtering may etch a surface by bombardment with ions. Wet Etch differs from dry etching in that it may use a liquid and/or chemical action to remove material with minimal, if any, physical etching
Some support layers or oxide layers may be more difficult to remove than others may. For instance, silicon oxide may be removed easily at a relatively low temperature. But, for example, aluminum oxide, having a relatively increased chemical stability, heat resistance and rigidity, may be more difficult to remove or may require harsher removal methods. Increased chemical stability may increase the difficulty of removal by a wet etch method. Further, removing material from polycrystalline materials may be easier relative to single crystals and quasi-single crystals. The increased strain at a grain boundary interface in polycrystalline materials, for example, may make the materials relatively more susceptible to chemical attack, particularly at the interface. Accordingly, etchants useful for polycrystalline materials sometimes may not be useful as etchants for single crystals and quasi-single crystals of the same or similar chemical composition.
Increased rigidity for crystals may make dicing and/or grinding of those crystals relatively more problematic. Dicing forcibly pushes a blade through a laminate between layers. Grinding physically abrades the surface. Increases in broken and damaged laminates may result as increasingly rigid laminates are used.
With the removal of some or all of a support layer, the freestanding semiconductor layer may be used in optoelectronic devices such as light emitting diodes and lasers. Such devices using freestanding gallium nitride semiconductor layers may emit blue light and UV laser, possibly enabling a relatively higher storage density in magneto-optic memories and CD-ROM's and the construction of full color light emitting displays.
It may be desirable to have one or more of an etchant, a method for using the etchant, an etched laminate or a freestanding crystal, and a device containing the etched laminate or the freestanding crystal.